A blog to share security, networking and cloud related technology information as @vCloudernBeer picked up on his search for his destiny in the cloud. (LinkedIn: https://www.linkedin.com/in/chowanthony)

Wednesday, November 5, 2014

OpenStack Series: Part 5 – Glance – Image Service

OpenStack Image Service offers retrieval, storage, and metadata
assignment for the images used by Nova.

OpenStack Object Storage allows users to store and retrieve images through a simple
Web Service (ReST: Representational State Transfer) interface.

Glance works hand in hand with Nova to provide support for virtual machine provisioning. It also has interaction with Keystone for API authentication.

Glance accepts API requests for images (or image metadata) from end
users or Nova components and can store its disk files in the object
storage service, Swift or other storage repository.

A more comprehensive list of disk and container format supported int he storage repository can be found here:

Disk Format

The disk format of a virtual machine image is the format of the underlying
disk image. Virtual appliance vendors have different formats for laying out
the information contained in a virtual machine disk image.

You can set your image’s disk format to one of the following:

raw

This is an unstructured disk image format

vhd

This is the VHD disk format, a common disk format used by virtual machine
monitors from VMWare, Xen, Microsoft, VirtualBox, and others

vmdk

Another common disk format supported by many common virtual machine monitors

vdi

A disk format supported by VirtualBox virtual machine monitor and the QEMU
emulator

iso

An archive format for the data contents of an optical disc (e.g. CDROM).

qcow2

A disk format supported by the QEMU emulator that can expand dynamically and
supports Copy on Write

aki

This indicates what is stored in Glance is an Amazon kernel image

ari

This indicates what is stored in Glance is an Amazon ramdisk image

ami

This indicates what is stored in Glance is an Amazon machine image

Container Format

The container format refers to whether the virtual machine image is in a
file format that also contains metadata about the actual virtual machine.

You can set your image’s container format to one of the following:

bare

This indicates there is no container or metadata envelope for the image

Another good feature from this oVirt integration with Glance is that oVirt can "discover" the size of the QCOW2 image by looking into the QCOW2 header. Glance metadata does not provide the size of the image.

Glance API

API has an important role in Glance for image processing. Check here for a deeper discussion of the Glance API.

There are 2 versions of Glance API - version 1 and version 2. Glance API version 2 provides standardization of some custom properties of the image.

Glance depends on Keystone and the OpenStack Identity API to handle
authentication of clients. You must obtain an authentication token from
Keystone using and send it along with all API requests to Glance through
the X-Auth-Token header. Glance will communicate back to Keystone to
verify the token validity and obtain your identity credentials.